Electronic imaging devices such as digital cameras are used in a wide range of applications and are steadily becoming less expensive and simpler to use. Electronic images have many advantages over film-based images that are causing the use of electronic imaging devices to rapidly increase. Electronic images may be stored indefinitely without the image degradation suffered by film-based images. Electronic images can be viewed immediately after capture and used in a variety of ways such as printing, posting to a web page on the World Wide Web, transmitting to others by electronic mail (email) or other means, etc. As the capacity of removable solid-state memories has increased and price has gone down, typical electronic imaging devices can now capture and store hundreds of electronic images. Electronic images can also be previewed and stored or deleted in the electronic imaging device as desired.
Electronic imaging devices, such as digital cameras, typically convert light to electrical signals using a two dimensional photodetector. Commonly used photodetectors contain a two dimensional array of millions of light-sensitive cells, each capturing one picture element (or pixel) of an image. As an image is focused onto the photodetector, an electrical charge builds up in the photodetector cells. The magnitude of the electrical charge corresponds to the intensity of the image light—brighter light generates a larger electrical charge. Thus, the image light focused on the photodetector generates a pattern of varying electrical charges across the photodetector. The magnitude of the electrical charges across the photodetector are analyzed and stored in the electronic imaging device as an electronic representation of the image. In an electronic imaging device such as a digital camera, the magnitudes of the electrical charges are converted into numerical data in an analog to digital (A/D) converter.
One weakness of photodetectors is that they are susceptible to aliasing, causing incorrect colors or structure in the final image in high frequency regions. If the image contains fine detail causing pixel values to vary widely from one pixel to the next, this high frequency content may be missed or misinterpreted by the photodetector. Color errors are a particularly common type of aliasing. Conventional electronic images represent color by providing a red (R), green (G) and blue (B) color value for each pixel, which are combined when displayed or printed to produce the actual color for that location. However, commonly used photodetectors do not measure a red, green and blue value at each pixel. Rather, color photodetectors typically include a color filter over each pixel so that each captures only one of the three colors. The two missing color values for each pixel are estimated based on neighboring pixels. If the fine detail of the image lands only on one pixel and not its neighbors, the estimation of the two missing color values for that pixel will be incorrect. Thus, the discrete nature and the limited number of pixels, and the fact that each pixel is filtered to sample only one color, may result in aliasing.